3-6.2.8 Intercalation between bases

The planar structure of chemicals such as ethidium bromide and proflavine allows them to insert between stacked bases in ds DNA. This insert causes the DNA's backbone to stretch and makes slippage during replication more likely to occur since the bonding between the strands is made less stable by the stretching. Forward slippage results in deletion mutation, while reverse slippage results in an insertion mutation. The intercalation of anthracyclines such as daunorubicin and doxorubicin also interferes with the functioning of the enzyme topoisomerase II, blocking replication as well as causing mitotic homologous recombination.

3-6.2.9 Backbone damage

Ionizing radiations may produce highly reactive free radicals that can break bonds in the DNA. Double-stranded breakages are particularly damaging and tough to repair, forms translocation and deletion of part of a chromosome. Alkylating agents like mustard gas cause breakages in the DNA backbone. Oxidative stress produces highly reactive oxygen species (ROS) which cause damage to DNA. Incorrect repair of other damages induced by the highly reactive species also lead to mutations.

3-6.2.10 T-DNA mediated mutagenesis

Transfer-DNA (T-DNA) insertion is a highly effective mutagen for genome-wide mutagenesis (Krysan et al. 1999). It has been widely exploited to produce insertion mutants in Arabidopsis thaliana for functional characterization of the every gene in the genome. Even if mRNA is transcribed, T-DNA sequence may contain stop codons, resulting in early translation termination (Krysan et al. 1999). Although it is not an ideal technique, T-DNA insertion mutagenesis has been a powerful technique to link genes to phenotypes

For plant system, homologous recombination machinery is not very effective. Moreover, active transposons do not exist in every species including Arabidopsis. Under such limitations, T-DNA mediated insertional mutagenesis provides a suitable tool for insertional mutagenesis. T-DNA is the transferred DNA from tumour inducing plasmid from Agrobacterium sp. T-DNA is widely used for successful transformation in plants. During T-DNA mediated transformation, the mutated locus also gets tagged which helps further isolation of the mutated gene.